Aluminum cans are used primarily as containers for retail sale of beverages in individual portions. Annual sales of such cans are in the billions and consequently, over the years, their design has been refined to reduce cost and improve performance. Other refinements have been made for ecological purposes, to improve reclamation and promote recycling.
Cost reductions may be realized in material savings, scrap reduction and improved production rates. Performance improvements may be functional in nature, such as better sealing and higher ultimate pressure capacity. Such improvements can allow the use of thinner sheet metal, which leads directly to material cost reductions. Performance improvements may also be ergonomic in nature, such as a can end configured to allow for easier pull tab access or better lip contact.
Aluminum cans are usually formed from a precoated aluminum alloy, such as the aluminum alloy 5182. The cans, which are typically made from relatively thin sheet metal, must be capable of withstanding pressures approaching 100 psi, with 90 psi being an industry recognized requirement. The cans are usually formed from a can body to which is joined a can lid or closure. Each of these components has certain specifications and requirements. For instance, the upper surface of the can lids must be configured to nest with the lower surface of the can bottoms so that the cans can be easily stacked one on top of the other. It is also desirable to have the can lids themselves nest with each other in a stacked arrangement for handling and shipping purposes prior to attaching the can lid to the can body. The ability to satisfy these functional requirements with the use of ever less material continues to develop.
Patent Cooperation Treaty International Publication Number WO 96/37414 describes a can lid design for reduced metal usage. This can lid comprises a peripheral portion or “curl,” a frustoconical chuckwall depending from the interior of the peripheral curl, an outwardly concave annular reinforcing bead or “countersink” extending radially inwards from the chuckwall, and a center panel supported by the inner portion of the countersink. The frustoconical chuckwall is inclined at an angle of between 20° and 60° with respect to an axis perpendicular to the center panel. The chuckwall connects the countersink and peripheral curl and is the portion of the lid the seaming chuck contacts during the seaming process. A double seam is formed between the can end and a can body by a process wherein the peripheral curl is centered on the can body flange by a chuck that is partially frustoconical and partially cylindrical. The frustoconical portion of the chuck is designed to contact the frustoconical chuckwall of the can lid. The overlap of the peripheral curl on the lid with the can body flange is described to be by a conventional amount. Rotation of the can lid/can body, first against a seaming roll and then a flattening roll completes a double seam between the two parts. During the flattening portion of the operation, the portion of the chuckwall adjacent to the peripheral curl is bent and flattened against the cylindrical surface of the chuck. The lid of International Publication Number WO 96/37414 incorporates known dimensions for the peripheral curl portion which is seamed to the can.
The can lid of International Publication Number WO 96/37414 is also susceptible to increased metal deformation during seaming and failure at lower pressures. U.S. Pat. No. 6,065,634 (Brifcani), describes the same can lid design as described in International Publication Number WO 96/37414.
Another Patent Cooperation Treaty International Publication, Number WO 98/34743, describes a can lid design which is a modification of the WO 96/37414 can lid wherein the chuckwall is in two parts. This can lid comprises a peripheral portion or “curl,” a two-part chuckwall depending from the interior of the peripheral curl, an outwardly concave annular reinforcing bead or “countersink” extending radially inwards from the chuckwall, and a center panel supported by the inner portion of the countersink. The first part of the chuckwall is frustoconical and adjacent to the curl, and is inclined to an axis perpendicular to the central panel at an angle between 1 and 39 degrees, typically between 7 and 14 degrees. The second part of the chuckwall is frustoconical and adjacent to the reinforcing bead, and is inclined to an axis perpendicular to the central panel at an angle between 30 and 60 degrees, preferably between 40 and 45 degrees. A double seam is formed between the can end and a can body by a process wherein the peripheral curl is centered on the can body flange by a two-part chuck having frustoconical and cylindrical portions as in WO 96/37414. Rotation of the can lid/can body, first against a seaming tool and then a flattening roll completes a double seam between the two parts. During the seaming operations, the first portion of the chuckwall, adjacent to the peripheral curl, is deformed to contact the cylindrical surface of the chuck.